/*
 * Copyright 2002-2014 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.hotswap.agent.util.spring.io.loader;

import org.hotswap.agent.util.spring.io.resource.Resource;
import org.hotswap.agent.util.spring.util.ResourceUtils;


/**
 * Strategy interface for loading resources (e.. class path or file system
 * resources). An {@link org.springframework.context.ApplicationContext} is
 * required to provide this functionality, plus extended
 * {@link org.hotswap.agent.util.spring.path.springframework.core.io.support.ResourcePatternResolver}
 * support.
 *
 * <p>
 * {@link DefaultResourceLoader} is a standalone implementation that is usable
 * outside an ApplicationContext, also used by {@link ResourceEditor}.
 *
 * <p>
 * Bean properties of type Resource and Resource array can be populated from
 * Strings when running in an ApplicationContext, using the particular context's
 * resource loading strategy.
 *
 * @author Juergen Hoeller
 * @since 10.03.2004
 * @see Resource
 * @see org.hotswap.agent.util.spring.path.springframework.core.io.support.
 *      ResourcePatternResolver
 * @see org.springframework.context.ApplicationContext
 * @see org.springframework.context.ResourceLoaderAware
 */
public interface ResourceLoader {

    /** Pseudo URL prefix for loading from the class path: "classpath:" */
    String CLASSPATH_URL_PREFIX = ResourceUtils.CLASSPATH_URL_PREFIX;

    /**
     * Return a Resource handle for the specified resource. The handle should
     * always be a reusable resource descriptor, allowing for multiple
     * {@link Resource#getInputStream()} calls.
     * <p>
     * <ul>
     * <li>Must support fully qualified URLs, e.g. "file:C:/test.dat".
     * <li>Must support classpath pseudo-URLs, e.g. "classpath:test.dat".
     * <li>Should support relative file paths, e.g. "WEB-INF/test.dat". (This
     * will be implementation-specific, typically provided by an
     * ApplicationContext implementation.)
     * </ul>
     * <p>
     * Note that a Resource handle does not imply an existing resource; you need
     * to invoke {@link Resource#exists} to check for existence.
     * 
     * @param location
     *            the resource location
     * @return a corresponding Resource handle
     * @see #CLASSPATH_URL_PREFIX
     * @see org.hotswap.agent.util.spring.io.resource.springframework.core.io.Resource#exists
     * @see org.hotswap.agent.util.spring.io.resource.springframework.core.io.Resource#getInputStream
     */
    Resource getResource(String location);

    /**
     * Expose the ClassLoader used by this ResourceLoader.
     * <p>
     * Clients which need to access the ClassLoader directly can do so in a
     * uniform manner with the ResourceLoader, rather than relying on the thread
     * context ClassLoader.
     * 
     * @return the ClassLoader (only {@code null} if even the system ClassLoader
     *         isn't accessible)
     * @see org.springframework.util.ClassUtils#getDefaultClassLoader()
     */
    ClassLoader getClassLoader();

}